1. Field of the Invention
The present invention relates to an improvement of an apparatus for applying a liquid material onto a predetermined portion, such as a pen (e.g., a ballpoint pen, a felt-tip pen, and the like) using a water-base ink or other types of ink, or a tool for applying cosmetics or medicines, and the like. More specifically, the present invention relates to a pen storing a water-base ink, such as a ballpoint pen, a felt-tip pen, and the like, that can store a large quantity of water-base ink, can satisfactorily control a quantity of ink to be supplied, and can reliably prevent scratching without ink and ink dripping caused by changes in temperature, atmospheric pressure, and the like.
2. Prior Art
Recently, ballpoint pens, felt-tip pens, and the like employing a water-base ink have been widely used.
In these conventional ballpoint pens, a fibrous member such as cotton is filled in an ink reservoir in a cylindrical casing, and is impregnated with ink. For this reason, only a small quantity of ink can be held. Since a small quantity of ink is supplied to a writing tip of the ballpoint pen or felt-tip pen, if a user writes fast, the ink is not often applied to the predetermined portion.
In order to eliminate these drawbacks, some pens store liquid ink directly in their cylindrical casings. However, in these pens, as the ink in an ink reservoir is consumed, air must be accordingly introduced therein. However, with this structure, the air in the ink reservoir expands due to changes in temperature, atmospheric pressure, and the like, thus easily causing dripping from a writing tip.
In some pens, an elongated, cylindrical, ink reservoir is used to store an ink therein, and a slidable plug, which slides to keep a liquid-tight seal, is inserted in the ink reservoir, to separate the ink from air in the ink reservoir and to communicate the air therein with outer air. As the ink is consumed, the slidable plug slides.
With this structure, a large quantity of ink can be stored, and ink dripping due to expanded air can be prevented. For example, in the case of a ballpoint pen using a water-base ink, a suction pressure, with which a writing tip draws the internal ink upon writing, corresponds to a pressure head of about 200 mm. Therefore, a slide resistance of the slidable plug must be set in a range below a pressure head of 200 mm. If the slide resistance of the slidable plug increases, a large pressure difference must be generated between the ink and air so as to move the slidable plug. For this reason, if the ink expands due to a change in temperature, a pressure of the ink portion becomes higher than the atmospheric pressure. Contrary to this, if the ink portion shrinks due to a change in temperature, the pressure of the ink portion becomes lower than the atmospheric pressure. For these reasons, in a pen having the slidable plug, dripping may occur, or air is drawn from the writing tip and writing fails to perform due to ink shortage. If such a pen falls on a floor or a desk, an instantaneous pressure difference is caused in the ink portion due to inertia acting thereon, and similar drawbacks to the above occur. In order to eliminate these drawbacks, the slide resistance of the slidable plug is so increased as to cancel the inertia acting on the ink portion. For this purpose, the slide resistance of the slidable plug must be accurately determined. However, it is difficult to accurately control the slide resistance of the slidable plug, and the structure of the slidable plug becomes complicated.
In the pen having the slidable plug, a mechanism for accurately controlling the flow rate of ink supplied to a writing tip must be added.
As the conventional ink-supply flow rate control mechanism, a fibrous core, as hardened fibers, is used. In this mechanism, the ink is supplied to the writing tip by a capillary attraction of the fibrous core, and excessive ink supply can be prevented by the flow resistance in the fibrous core. The flow rate of the ink is controlled by a density of the fibrous core.
However, with this mechanism, a flow rate of ink cannot be reliably controlled, and ink dripping or scratching without an ink, i.e., scratchy writing due to insufficient ink, cannot be satisfactorily prevented.